Method for preventing corrosion of hydrogen chloride burners and coolers



Sept. 15, 1942. MAUDE 2,295,591

METHOD FOR PREVENTING CORROSION OF HYDROGEN CHLORIDE BURNERS AND COOLER-S Filed Feb. 29, 1940 Fig.1

INVENT OR.

W M W W ATTORNEY.

Patented Sept. 15, 1942 METHOD FOR PREVENTING CORROSION OF HYDROGEN CHLORIDE BURNERS AND COOLERS Aylmer H. Maude, Niagara Falls, N. Y., assignor to Hooker Electrochemical Company, Niagara Falls, N. Y., a corporation of New York Application February 29, 1940, Serial No. 321,600

8 Claims. (01. 23-156) .the temperature of the burner and cooling surfaces so thatmoisture that may be present, due

' to moisture in the chlorine or hydrogen or traces not only in considerable expense for renewals but also in frequent interruption of production. More-over, such materials are not well adapted to formation of air tight joints in and around the burner and burner connections. If such burners were to be operated at pressures above atmospheric there would be a leakage of H01 gas which would be highly objectionable. It is practically necessary, therefore, to operate under a slight negative pressure. This results in infiltration of air, which causes a part of the hydrogen to burn to H2O, reducing the yield of HCl. In the course of the cooling, this moisture condenses while the gas is still quite hot. This necessitates dealing with hot moist hydrogen chloride, which is chemically very active. The product therefore becomes contaminated with iron, if any. be present in the ceramic material used in the apparatus, as is very likely to be the case. Furthermore, since refractory materials are in general very poor conductors of heat the apparatus which must be installed for cooling the HCl gas, when constructed of such material, is necessarily quite bulky and occupies much space.

I am aware that it has been proposed to burn hydrogen and chlorine together in a metal burner, by supplying the gases to the burner under such pressure that the resulting velocity is greater than the velocity of flame propagation, so that the flame is prevented from actual contact with the burner tip. This practice is objectionable for the following reasons: In the first place, if the hydrogen and chlorine are of electrolytic origin,

as is very likely to be the case, it becomes necessary to compress both these gases to a substantial pressure, which involves considerable expense. In the second place, the velocity necessary to keep the flame from contact with the burner tip without extinguishing it is quite critical and, even with good control, the flame is liable to become extinguished. This of course causes the cooling system to become filled with an explosive gaseous mixture within the space of a few seconds.

of oxygen in the gases, will not be condensed. The remaining heat of reaction can then be extracted in relatively small coolers constructed of special metal, such as tantalum, which is resistant to wet HCl. I have found that it is possible to accomplish these objectives by constructing the burner of a metal that is a very'good conductor of heat and making it relatively massive so as to provide a considerable mass of metal to absorb the heat and a large cross section of metal relative to that of the gas passage and burner tip to carry the heat away. I find that it is perfectly possible to do this withoutwatcr cooling, but in practice I prefer to cool somewhat by flowing water through comparatively small passages, for the reason that this enables me to make use of thermostatictemperature control, which is very important for the reasons given above, namely in order to avoid cooling the surfaces to a point at which moisture would condense upon them. This" temperature is a function of the moisture content of the gas, which varies somewhat, as will be shown later.

In practice, some slight oxidation of the metal may give rise to formation of its chloride. If a liquid film saturated with metal chloride were allowed to form on the metal surface, it would have a vapor pressure lower than that of the condensate. This film would therefore dry with difflculty. To avoid this'it is necessary to operate at a temperature a few degrees higher than that at which moisture condenses. If the metal forms a deliquescentchloride this differential must be greater than otherwise. Thus if the metal be iron which forms a deliquescent chloride, the burner must be kept at least 15 C. above the dew point of the gases, whereas if the metal be copper, which forms a non-deliquescent chloride, a differential of 3 C. is sufiicient. Copper is also a very superior conductor of heat. I have therefore found it to be one of the metals best suited for construction of my burner.

Referring to the drawing:

Figure l is a diagram of my apparatus including the burner and cooler.

Figure 2 is a side elevation of the same, likewise in section.

Figure 3 is a side elevation of the same, likewise in section.

In the figures, I is a massive bar, preferably of copper, which forms the body of my burner. 2 is a passage bored therethrough for the gases, extending longitudinally through the body I from one end to near the other end, where it preferably makes a right angled turn, for reasons that will hereinafter appear, issuing through one sideof the bar. The open end of passage 2 forms the burner tip 3. The other end 4 of passage 2 is threaded for reception of pipe nipple 5. Nipple 5 has welded to it at one side as by weld 6, pipe connection I, through which hydrogen is admitoutside diameter of which is slightly smaller than that of the inside of nipple 5 and also of passage 2. Pipe 8 is concentric with passage 2 and nipple 5 and is welded to the latter at its outer end as by weld 9, forming with it as well as with passage 2 an annular passage I 0. Pipe 8 extends through passage 2 for the greater part of its length, but terminates .at II short of the angle in passage 2. Passage I2 is drilled longitudinally down one side of .bar I parallel to passage 2, across the inner end beyond the angle in passage 2, and back up the other side of bar I, again parallel to passage 2, with an inlet and an outlet forjcooling water at I3, I3. Bar I is provided with flange I4 for securing the burner in position in the apparatus with which it is associated as hereinafter explained. The burner as a whole will be hereinafter referred to as II4.

Referring to Figure 3, burner I--I4 is let into the side of combustion chamber I5 through neck I6, to which it is secured by flange IT and its own flange I4. The burner tip 3 is aligned co-axially with combustion chamber I5.

Hydrogen is admitted to burner I-I4 through pipe 'I from a source not shown. It is controlled by shut off valves I8, I8 and regulated by calibrated orifice tube I9 co-operating with means such as a gasometer (not shown) for maintaining a constant moderate pressure on orifice I 9. Chlorine is admitted to burner I-Il4 through pipe 8 from a source not shown. It is controlled by shut off valves 2|], and calibrated orifice tube 2| cooperating with means such as a gasometer (not shown) for maintaining a constant moderate pressure on orifice 2I. The construction and mounting of orifice tubes I8 and 2I will be selfevident from the drawing.

Combustion chamber I5, which is relatively elongated, is provided with frangible discs 22 at either end, as a safeguard against disruption of the apparatus in case of explosion in starting up the burner or otherwise. In explosions of this character the gases acquire such high kinetic energy that they will not turn angles but exert their force in a straight line. Consequently, to be effective, the frangible device must be at the ends of a straight combustion chamber as shown. This makes it necessary to let the burner in through the side of the combustion chamber, hence the angle in passage 2 of the burner... The frangible discs are claimed in divisional application Serial No. 418,585, filed Nov. 10, 1941.

Combustion chamber I5 is provided with water iacket 23. The exit from combustion chamber I5 is by way of pipe 24 which may make a reverse bend as indicated. Pipe 24 is also jacketed at 25, as shown. The cooling water'is circulated through jackets 23, 25 by pump 26, from tank admitted through pipe 29 thermostat 3| is there-.

fore able to control the temperature of the water in tank 21 and thus the temperature'of the water in jackets 23, 25. The flow through the jackets is purposely made so great that the temperature of the cooling water is only slightly raised. Hence there is no need to employ the counter-flow principle of heat transfer and the walls of the combustion chamber I5 and pipe 24 are maintained at a temperature very close to that of the water. Some of the cooling water is by-passed through passage I2 of burner I-I4 through pipe 33 controlled by valves 34, 34. The flow of water through passage I2 may also be regulated by throttling the flow through the main system as by valve 35.

From pipe 24 the products may pass to the tantalum cooler referred to above (not shown) and if desired then absorbed in water. The cross section of bar I should preferably be 8 to 10 times that of passage 2 and the burner tip should issue from the side of the bar at a distance of not less than its diameter from the end of the bar, in order that the heat which radiates from the flame back to the burner may be carried away by the metal of the burner with the aid of only sufficient water cooling as will serve to maintain control over the temperature of the burner walls. With the burner proportioned as thus indicated, the velocity of the gases at the burner tip is preferably from 4 to 40 feet per second but may be outside theselimits.

The following table will serve to show the dew point of H01 gases of different moisture content:

Moisture, percent by volume Dew point As stated above, the moisture content of the gas depends upon the moisture and oxygen content of the hydrogen and chlorine, which in turn depends upon how carefully these gases have been dried and the precautions that have been observed to exclude air, such as avoidance of negative pressures such as could cause infiltration through pipe joints. In practice I find that 'the moisture content may be 0.5 to 10 percent, or more typically 1 to 3 percent. The corresponding dew points are 28* C., 71 C., 37 C. and 53 C. respectively. As stated above; if the apparatus is of copper the cooling water should be kept at least 3 C. above these temperatures, while if it is of iron the cooling water should be not less than 15 C. and preferably 20 C. above these temperatures. The upper limit of temperature for the cooling water may belts boiling point at atmospheric pressure.

However, I do not wish to be limited to the exact range of temperatures given herein. Neither do I wish to be limited to the exact type of construction illustrated as many modifications in detail will suggest themselves to those skilled in the art.

Although I have chosen the synthesis of hydrogen chloride to illustrate my method and apparatus I do not wish to be limited thereto as other similar reactions will suggest themselves to persons skilled in the art, such as the analogous synthesis of hydrogen bromide; controlled reaction of acetylene with chlorine to form dichlorcthyleneor tetrachlorethane; controlled reaction of acetylene or natural gas with oxygen to produce carbon black; controlled reaction of hydrogen sulphide with oxygen to form sulphur dioxide or combustion of any fuel gas, as in high temperature oxy-hydrogen or oxy-ac-etylene furnaces.

I claim. as my invention:

1. The method of protecting the surfaces of metallic burner tips in contact with hot chlorine and hot humid hydrogen chloride and the metallic combustion chambers in which the chlorine is burned with hydrogen, producing hydrogen tallic combustion chambers in which the chlorine is burned with hydrogen, producing hydrogen chloride having a dew point not materially above 71 C., with cooling by means of water from a source at a temperature below said dew point, which comprises applying heat .to the water to raise it to an initial temperature sufliciently above said dew point to avoid condensation of water in presence of the chloride of the metal, but well below its boiling point, and causing it to'fiow in effective cooling relation through the metal with said surfaces, flowing generally from zones of higher temperature toward zones of lower temperature, at velocities everywhere precluding rise in temperatures of the water to its boiling point.

5. The method of protecting the surfaces of metallic burner tips in contact with hot chlorine and hot humid hydrogen chloride and of the metallic combustion chambers in which the chlorine is burned with hydrogen, producing hydrogen chloride having a dew point not materially above 71 C., which comprises maintaining a body of cooling liquid at a temperature chloride having a .dew point not materially above rise in temperature of the water to its boiling point.

2. The method of protecting the surfaces of metallic burner tips in contact with hot chlorine and hot humid hydrogen chloride and of the metallic combustion chambers in which the chlorine is burned with hydrogen, producing hydrogen chloride having a dew point not materially above 71C., with cooling by means of water from a source at a temperature below said dew point, which comprises applying heat to the water to raise it to an initial temperature sufilcientiy above said dew point to avoid condensation of water in presence of the chloride of the metal, but well below its boiling point, and causing it to flow in efiective cooling relation through the metal with said surfaces, at velocities everywhere precluding substantial rise in temperature of the water.

3. The method of protecting the surfaces of metallic burner tips in contact with hot chlorine and hot humid hydrogen chloride and of the metallic combustion chambers in which the chlorine is burned withhydrogen, producing hydrogen chloride. having a dew point not materially above 71 C., with cooling of the surfaces by means of water from a source at a temperature below said dew point, which comprises applying heat to the water to raise it to an initial temperature suflisufiiciently above said dew point to avoid condensation of water in presence of the chloride of the metal, but well below C., causing liquid from said-body to flow in effective cooling relation through the metal with said surfaces, at velocities everywhere precluding rise in temperature of the liquid to 100 0., recycling the liquid to said body and withdrawing heat to maintain said body at the desired temperature. 6. The method of protecting the surfaces. of

metallic burner tips in contact with hot chlorine and hot humid hydrogen chloride and of the metallic combustion chambers in which the chlorine is burned with hydrogen, producing hydrogen chloride having a dew point not materially above 71 C., which comprises maintaining a body of water at a temperature sufllciently above said dew point to avoid condensation of water in presence of the chloride of the metal, but well below its boiling point, causing water from said body to flow in effective cooling relation through the metal with said surfaces at velocities everywhere precluding rise in temperature of the water to its boiling point, recycling the water to said body, adding colder water to maintain said body at the desired temperature and allowing excess water to go to waste.

'7. The method of protecting the surfaces of burner tips and combustion chambers formed of metals whose chlorides are non-deliquescent, in contact with hot chlorine and hot humid gaseous hydrogen chloride produced by combustion therein of the chlorine with hydrogen and having a dew point not materially above 71 C., with cooling by means of water from a source at a temperature below said dew point, which comprises applying heat to the water to raise it to an initial temperature sufficiently above said dew point to avoid condensation of water in presence of the chloride-of the metal, but well below its boiling point, and causing it to flow in effective cooling relation through the metal with said surfaces, at

velocities at which said surfaces are cooled to a temperature not below substantially three degrees above said dew point.

8. The method of protecting'the surfaces of burner tips and combustion chambers formed of metals whose chlorides are deliquescent, in contact with hot chlorine and hot humid gaseous hydrogen chloride produced by combustion therein of the chlorine with hydrogen and having a dew point not materially above 71 0., with cooling by means oil-water from a source at a temperature below said dew'point, which comprises applying heat to the water to raise it to an initial temperature suiilciently above said dew point .to avoid condensation of water in presence or the chloride 01' the metal, but well pelow its boiling point, and'causing it to flow in eflective cooling relation through the metal with said surfaces, at velocities at which said surfaces are cooled to a temperature not below substantially fifteen de-. '8 grees above said dew point.

AYLMER H. MAUDE. 

